# libprojfs **Repository Path**: mirrors_github/libprojfs ## Basic Information - **Project Name**: libprojfs - **Description**: Linux projected filesystem library - **Primary Language**: Unknown - **License**: LGPL-2.1 - **Default Branch**: master - **Homepage**: None - **GVP Project**: No ## Statistics - **Stars**: 0 - **Forks**: 0 - **Created**: 2020-08-08 - **Last Updated**: 2026-02-14 ## Categories & Tags **Categories**: Uncategorized **Tags**: None ## README # libprojfs A Linux projected filesystem library, similar in concept to the Windows [Projected File System][winprojfs] and developed in conjunction with the [VFSForGit][vfs4git] project. While the libprojfs C library may also be used independently of VFSForGit, our primary goal is to enable users to run the VFSForGit client on a Linux system. **PLEASE NOTE:** At present libprojfs is undergoing rapid development and its design and APIs may change significantly; some features are also incomplete, and so we do not recommend libprojfs for any production environments. However, we wanted to share our progress to date, and we hope others are as excited as we are at the prospect of running the VFSForGit client on Linux in the not-too-distant future! ## Current Status | Branch | Functional Tests | | :--------: | :-------------------------------------------------------: | | **master** | [![CI status: master][ci-master-status]][ci-master-redir] | The library is under active development and supports basic directory projection, with additional features added regularly. We will only make a first, official versioned release once initial development is complete. A libprojfs filesystem can currently be used to mount a VFSForGit [`MirrorProvider`][vfs4git-mirror] test client; we expect to continue our pre-release development until the VFSForGit client proper is also functional with libprojfs, at which point we may make an initial tagged release. ## Design The libprojfs library is designed to function as a stackable Linux filesystem supporting a "provider" process which implements custom callbacks to populate files and directories on demand. This is illustrated in the context of a VFSForGit provider below: ![Illustration of libprojfs in provider context](docs/images/phase1.png) Actual file storage is delegated to a "lower" storage filesystem, which may be any Linux filesystem, e.g., ext4. At the time when a libprojfs filesystem mount is created, there may be no files or directories in the lower filesystem yet. As normal filesystem requests are made within the libprojfs mount (e.g., by `ls` or `cat`), libprojfs intercepts the requests and queries the provider process for the actual contents of the file or directory. The provider's response is then written to the lower filesystem so future accesses may be satisfied without querying the provider again. See our [design document][design-linux] for more details. We anticipate that whether libprojfs remains a [FUSE][fuse-man]-based library, or becomes a [libfuse][libfuse]-like interface to a Linux kernel module, it may be useful for purposes other than running a VFSForGit client. For this reason, we have tried to ensure that our native [event notification API](include/projfs_notify.h) is aligned closely with the Linux kernel's [fanotify][fanotify]/[inotify][inotify]/[fsnotify][fsnotify] APIs. ## Getting Started Please see our detailed [Build and Installation][build] page for step-by-step instructions on how to build and install libprojfs and its dependencies on Linux, and (optionally) also build and run the VFSForGit `MirrorProvider` test utility with libprojfs. So long as libprojfs remains based on [FUSE][fuse-man], the primary dependency for libprojfs is the user-space [libfuse][libfuse] library, as well as having the Linux [`fuse`][fuse-mod] kernel module installed. Support for [`user.*` extended attributes][xattr] must also be enabled on the "lower" storage filesystem. Your Linux kernel should have been compiled with the necessary configuration options (e.g., `CONFIG_EXT2_FS_XATTR` for [ext2/3/4][ext2]) and the underlying filesystem you use for libprojfs should be mounted with appropriate settings (e.g., [user_xattr][xattr-ext2] for ext2/3/4). If you are using a [Docker](https://www.docker.com) container, you may need to ensure the `fuse` kernel module is installed on your host OS, and `user.*` extended attributes are supported on your host's filesystem. See the [Using Docker containers][build-docker] section for more details. To test libprojfs with the Microsoft VFSForGit `MirrorProvider` (as we do not support the primary VFSForGit GVFS provider yet), .NET Core must be installed and parts of the VFSForGit project built. See the [Building and Running MirrorProvider][build-mirror] section for details. ## Contributing Thank you for your interest in libprojfs! We welcome contributions; please see our [CONTRIBUTING](CONTRIBUTING.md) guidelines and our contributor [CODE_OF_CONDUCT](CODE_OF_CONDUCT.md). ## Licensing The libprojfs library is licensed under the [LGPL v2.1](COPYING). See the [NOTICE](NOTICE) file for a list of other licenses used in the project, and the comments in each file for the licenses applicable to them. ## Development Roadmap We are developing the libprojfs library first, using FUSE to prototype and test its performance, before migrating functionality into a Linux kernel module (assuming that proves to be necessary to meet our performance criteria). For more details on the planned development phases, see our [design document][design-process]. ## Authors The libprojfs library is currently maintained and developed by several members of GitHub's Engineering organization, including: * [@chrisd8088](https://github.com/chrisd8088) * [@kivikakk](https://github.com/kivikakk) * [@wrighty](https://github.com/wrighty) You can also contact the GitHub project team at [opensource+libprojfs@github.com](mailto:opensource+libprojfs@github.com). [build]: docs/build-install.md [build-docker]: docs/build-install.md#using-docker-containers [build-mirror]: docs/build-install.md#building-and-running-mirrorprovider [ci-master-redir]: https://dev.azure.com/asconnor/asconnor/_build/latest?definitionId=1&branchName=master [ci-master-status]: https://dev.azure.com/asconnor/asconnor/_apis/build/status/github.libprojfs?branchName=master [design-linux]: docs/design.md#vfsforgit-on-linux [design-process]: docs/design.md#development-process [ext2]: https://www.kernel.org/doc/Documentation/filesystems/ext2.txt [fanotify]: https://github.com/torvalds/linux/blob/master/include/uapi/linux/fanotify.h [fsnotify]: https://github.com/torvalds/linux/blob/master/include/linux/fsnotify_backend.h [fuse-man]: http://man7.org/linux/man-pages/man4/fuse.4.html [fuse-mod]: https://www.kernel.org/doc/Documentation/filesystems/fuse.txt [inotify]: https://github.com/torvalds/linux/blob/master/include/uapi/linux/inotify.h [libfuse]: https://github.com/libfuse/libfuse [winprojfs]: https://docs.microsoft.com/en-us/windows/desktop/api/_projfs/ [vfs4git]: https://github.com/Microsoft/VFSForGit [vfs4git-mirror]: https://github.com/Microsoft/VFSForGit/tree/features/linuxprototype/MirrorProvider [xattr]: http://man7.org/linux/man-pages/man7/xattr.7.html [xattr-ext2]: http://man7.org/linux/man-pages/man5/ext4.5.html#MOUNT_OPTIONS